A better insight into the functional organization of the substantia gelatinosa (SG) of the spinal cord would help clarify normal and pathological functions of somatosensory systems associated with pain, itch temperature, and some forms of touch. Deciphering SG organization demands understanding the properties and connections of each subtype of SG neuron. This proposal suggests an approach to efficiently target and study a particular subtype of SG neurons labeled with the green fluorescent protein (SG-GFP neurons). The experiments will compare the morphology, membrane properties, and functional features of the SG-GFP neurons with SG neurons not expressing this marker. Confocal microscopy will be used to assess the morphological features and connections of the SG-GFP neurons. Whole cell patch clamp techniques will be used to explore the membrane properties and the synaptic partners of these neurons. Immunocytochemistry will be used to determine the expression profiles of molecules with known SG functions. This information will be used to develop a concept of the function of the SG-GFP type of neurons in the SG organization.